1. Field of the Invention
The present invention relates to a cream solder inspection method which inspects whether or not the cream solder coated preliminarily on a printed circuit board is applied in a proper condition to solder an electronic part on a printed circuit board and achieves a more secure inspection about the cream solder by removing a non-soldered portion which causes irregular reflection such as silk-printed portion, wiring pattern and bare pad located in the vicinity of that cream solder from an image photographed with a camera, and an inspection apparatus therefor.
2. Description of the Related Art
For example, Japanese Patent Application Laid-Open No. 5-29674 has disclosed a conventional cream solder inspection method. According to this method, light having a wave length of less than 600 nm is irradiated to the cream solder formed on an electrode made of copper foil on the print circuit board from obliquely above and then, reflection light, reflected from the aforementioned printed circuit board is allowed to enter into a camera located above so as to obtain a bright/dark image. Then, the quality of cream solder applying area is determined according to this bright/dark image.
According to the aforementioned publication, the quality of cream solder applying area is determined irrespective of presence/absence of a solder coating portion such as solder leveler or the quality of the cream solder is determined based on two-dimensional information so as to inspect the three-dimensional shape of the cream solder.
As for a method for coating the printed circuit board with the cream solder, a metallic screen containing small holes formed at its positions corresponding to cream solder applying positions is placed such that the aforementioned holes coincide with a cream solder printing face of the printing board and after that, the cream solder is applied to the printing face through the aforementioned holes in the screen. After the coating of the solder is finished, the screen is lifted up so that the printed cream solder is left at their applying positions through the holes in the screen. Then, the coating of the cream solder is completed.
Under such a coating method for the cream solder, when the aforementioned screen is lifted up, the cream solder, which is applied to such a small area of a soldering area as seen in recent years, is scraped from a peripheral face of its top portion by an inner peripheral face of each hole in the screen as shown in FIG. 4(b) as compared to a normal shape of the solder shown in FIG. 4(a), so that the amount of the solder becomes insufficient.
When the cream solder having such a configuration is inspected according to the technology disclosed in the aforementioned publication, that is, even in case of a printed circuit board having no solder coating portion like the solder leveler, it is impossible to detect that the cream solder is insufficient.
Further, if there is a portion having no solder, such as silk-printed portion, wiring pattern and bare pad, in the vicinity of an inspection place, that is, there is a non-soldered portion, the non-soldered portion, which causes reflection like the soldered portion, is mixed in the photographed image of the cream solder. Thus, the method for inspecting the shape of the cream solder has such a problem that accurate detection of the cream solder is disabled.
The present invention intends to solve the above described problem and therefore, an object of the invention is to provide an inspection method for cream solder capable of inspecting applying condition of the cream solder securely by irradiating light to the cream solder from at least two directions alternately, capturing that reflected light with a camera, obtaining a difference between the captured images to detect the shape of the cream solder and detect insufficiency of the cream solder and further removing a non-soldered portion printed in the vicinity of the cream solder, and an apparatus therefor.
To achieve the above object, according to an aspect of the present invention, there is provided an inspection method for cream solder for determining whether or not the shape of the cream solder is appropriate based on the information about the height of the cream solder by irradiating light from substantially besides in two directions opposing each other through a lighting means to the cream solder so as to obtain at least two images and obtaining a difference between the obtained images.
According to a preferred embodiment of the present invention, light is irradiated to the cream solder from substantially besides in at least two directions opposing each other alternately through a lighting means so as to obtain at least two images, a difference between the obtained images is calculated to obtain the information about the height of the cream solder and then, based on the information of the height whether or not the amount of the cream solder is appropriate is determined.
According to another aspect of the present invention, there is provided an inspection apparatus for the cream solder comprising: camera disposed above a printed circuit board which is subject of inspection; lighting means disposed substantially in the lateral direction of the cream solder applied to the printed circuit board and for irradiating light to the cream solder in two directions opposing each other alternately; arithmetic operating portion which switches the lighting means to get a difference between at least two images taken with the camera to obtain a side inclined portion of the cream solder from the luminance introduced from the difference; and determining portion for determining whether or not the shape of the cream solder is appropriate by comparing the value of the side inclined portion obtained by the arithmetic operating portion with a preliminarily set reference value.
According to still another aspect of the present invention, there is provided an inspection apparatus for the cream solder comprising: camera disposed above a printed circuit board which is subject of inspection; lighting means disposed substantially in the lateral direction of the cream solder applied to the printed circuit board and for irradiating light to the cream solder in two directions opposing each other alternately; image processing means for counting dimensions and area of an image of the solder taken with the camera; arithmetic operating means for computing the dimensions and area counted by the image processing means to obtain the amount of the solder; and control means provided with a program for inspecting the shape of the solder to control the respective means.
According to a further aspect of the present invention, there is provided an inspection apparatus for the cream solder comprising: camera disposed above the printed circuit board which is subject of inspection; lighting means disposed substantially in the lateral direction of non-soldered portion such as silk-printed portion formed on the printed circuit board and for irradiating light to the non-soldered portion in two directions opposing each other alternately; and arithmetic operating portion which switches the lighting means to obtain a difference between at least two images taken with the camera and removes the non-soldered portion from the image.